[Bug target/83832] New: [RX] Improve bittests

["olegendo at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83832

            Bug ID: 83832
           Summary: [RX] Improve bittests
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: olegendo at gcc dot gnu.org
  Target Milestone: ---
            Target: rx*-*-*

If a bit test is done with only a single bit in the constant, the btst
instruction should be used to get smaller code.

When testing for constants such a 0xFF or 0xFFFF a zero_extend is emitted
followed by a compare against zero.  These 2 instructions can be folded into a
single tst instruction to improve execution speed.


These are just a few observations, probably there are more.

int bittest_0 (int x)
{
  return x & 0xFF ? 4 : 60;

  // 5b 11              movu.b  r1, r1
  // 61 01              cmp     #0, r1

  // better (speed):
  // fd 78 c1 ff 00     tst     #255, r1
}

int bittest_1 (int x)
{
  return x & 0xFFFF ? 4 : 60;

  // 5b 11              movu.b  r1, r1
  // 61 01              cmp     #0, r1

  // better (speed):
  // fd 78 c1 ff 00     tst     #255, r1
}

int bittest_2 (int x)
{
  return x & 0xFE ? 4 : 60;

  // fd 78 c1 fe 00     tst     #254, r1
}

int bittest_3 (unsigned int x)
{
  return x & (1 << 1) ? 4 : 60;

  // fd 74 c1 02        tst     #2, r1

  // better (code size):
  // 7c 11              btst    #1, r1
}

int bittest_4 (unsigned char* x)
{
  return *x & (1 << 1) ? 4 : 60;

// cc 1e                mov.b   [r1], r14
// fd 74 ce 02          tst     #2, r14

// better (code size):
// f4 11                btst    #1, [r1].b
}